Implement Eq and PartialEq for DashMap and DashSet

[noahbkim]

Hi, I was hoping to revisit #138, where you said

They aren't implemented because equality makes no sense for a concurrent map. Fundamentally you never really have to compare two and if you do, you're probably architecting your code in a non-optimal way.

I agree with this entirely in the context of real, running code, but am hoping to change your mind on the basis of testing. Providing equality methods makes writing test cases that reason about the contents of DashMap's and DashSet's much more concise, and testing is arguably the one scenario where ergonomics & readability clearly outweigh performance. Please consider giving users the option, even if you feel obligated to warn them against it, to use these traits.

Happy to make any tweaks and add documentation at your request. Thanks for all the work on this project!

[xacrimon]

Hm, yes. You're right, this is an angle I didn't consider when I surely should have.

Thanks for bringing this to my attention, I will merge this now, place a TODO to add a sentence or two in docs about this for tomorrow. Cheers mate.

[noahbkim]

Legend, thanks!!